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Electrocatalytic Oxidation of Formate with Nickel Diphosphine Dipeptide Complexes: Effect of Ligands Modified with Amino Acids



A series of nickel bis(diphosphine) complexes with dipeptides appended to the ligands were investigated for the catalytic oxidation of formate to carbon dioxide, a proton, and two electrons. Typical rates of approximately 7 s–1 were found, similar to that for the parent complex (ca. 8 s–1), with amino acid size and positioning contributing very little to the rate or operating potential. Hydroxy functionalities did result in lower rates, which were recovered by protecting the hydroxy group. The results suggest that the overall dielectric properties introduced by the dipeptides do not play an important role in catalysis, but free hydroxy groups do influence activity, implying contributions from intra- or intermolecular interactions. These observations are important in developing a fundamental understanding of the effect that an enzyme-like outer coordination sphere can have upon molecular catalysts.